HIROSHIMA – Hiroshima marked the 74th anniversary of its atomic bombing by the United States on Tuesday, with tens of thousands of people attending a ceremony at ground zero.

In a speech, Mayor Kazumi Matsui urged the government to join a U.N. treaty banning nuclear weapons.

But Prime Minister Shinzo Abe, also present, declined to do so, saying the treaty does not reflect security realities.

Japan is not alone in staying outside the treaty. Other countries under the U.S. nuclear umbrella have not signed up, and nor have the world’s nuclear-armed states.

“I call on the government of the only country to experience a nuclear weapon in war to accede to the hibakushas’ request that the TPNW be signed and ratified,” Matsui said, referring to the Treaty on the Prohibition of Nuclear Weapons.

“I urge Japan’s leaders to manifest the pacifism of the Japanese Constitution by displaying leadership in taking the next step toward a world free from nuclear weapons,” he said.

For the past two years, Matsui has stopped short of explicitly demanding that Japan join the treaty, citing his wish to not make political capital from the peace declaration. The treaty is not yet in force since it has not been ratified by the required 50 states.

Abe did not mention the treaty in his speech at the ceremony, but pledged instead that Japan will serve tenaciously as a “mediator between nuclear weapon states and non-nuclear weapon states” and “take the lead in making such efforts” in the international community.

Abe later told reporters the TPNW is “not based on the real aspects of security.”

This year’s anniversary came after the United States on Friday formally withdrew from the Intermediate-Range Nuclear Forces Treaty, a major nuclear arms control pact with Russia signed in 1987.

The move raised fears of a new arms race. It also builds on a slew of other security concerns including Iran’s nuclear activity and the standoff over North Korea’s nuclear weapons.

Such factors will play into how governments review the Nuclear Non-Proliferation Treaty, the keystone of the international nuclear disarmament regime, next spring.

Attended by some 50,000 people and representatives from about 90 countries including the United States, Russia and Britain, the annual memorial ceremony took place at the Peace Memorial Park near ground zero.

“Around the world today,” Matsui said, “we see self-centered nationalism in ascendance, tensions heightened by international exclusivity and rivalry, with nuclear disarmament at a standstill.”

The power of individuals is weak, he said, but added there have been many examples of collective strength achieving desired goals.

“Intolerance is itself a form of violence and an obstacle to the growth of a true democratic spirit,” the mayor said, quoting Mahatma Gandhi, the leader of India’s nonviolent independence movement against British rule.

He pointed out that “coming generations must never dismiss the atomic bombings and the war as mere events of the past.”

To convey the reality of the atomic bombing, a classical tanka poem, written by a woman who survived the bombing at the age of 5, was cited in the declaration for the first time.

U.N. Secretary General Antonio Guterres said in his message that “the world is indebted” to people in Hiroshima as well as Nagasaki, the other A-bombed city, “for their courage and moral leadership in reminding us all about the human cost of nuclear war.”

Pope Francis is scheduled to visit Hiroshima and Nagasaki in November during the first papal visit to Japan since John Paul II toured the country in February 1981.

Despite occasional heavy rain due to an approaching typhoon, residents and tourists began arriving at the Memorial Park from early morning.

Yasuo Kubo, 74, who experienced the bombing as a baby, offered a prayer as he does every morning. He said he feels “special” whenever the anniversary comes around.

“We must not go to war again. Everyone will understand that if they come here.”

Yumeka Yamamoto, a 19-year-old local university student, said classmates from other prefectures gave her questioning looks when she told them she planned to visit the park on the morning of the anniversary.

“I felt a bit sad. I want people outside Hiroshima to have more interest in (the atomic bombings),” she said.

A moment of silence was observed at 8:15 a.m., the exact time on Aug. 6, 1945, when a uranium-core atomic bomb named Little Boy dropped by a U.S. bomber exploded above Hiroshima.

Authorities estimate that roughly half of those who were around 1.2 kilometers from ground zero were killed that day, as well as between 80 and 100 percent of those who were within a 1.2 kilometer radius of the blast. By the end of that year, 140,000 people in total were estimated to have died as a result of the bombing.

A second atomic bomb was dropped on Nagasaki on Aug. 9 the same year. Japan surrendered six days later, leading to the end of World War II.

The combined number of surviving hibakusha from either bombing stood at 145,844 as of March, with their average age at 82.65.